In this application, it is proposed to complete the characterization of the major liver metabolite of retinol and of retinyl acetate. This compound is found in both "normal" and vitamin A-deficient rat liver, but the proportion of this compound to retinol and retinyl ester present is greatly reduced in the "normal" or vitamin A dosed animal. It is also proposed to continue the work on the use of protein bound retinol and/or retinoic acid in the differentiation of epithelial cells in cell or organ culture. We have shown that vitamin A is not required for growth of fibroblasts. Finally, the formation of certain specific proteins, low (or high) in vitamin A deficiency with regard to the specificity of vitamin A in the control of their synthesis.